Op-Amps and Saturation The Inverting Mode Op-Amp Rf R1 + V1 +Vs -Vs Vo 0V In theory, the gain of the op-amp is given by Rf ÷ R1. This equation works well until the output voltage increases too much. We must remember that the op-amp has a power supply. By increasing the input voltage, we find that the output voltage is limited. The op-amp cannot give out any more than about 85% of the voltage it is being supplied with (±15 V). We say that the op-amp saturates. Voltage Input / V -2 -1.6 -1.2 -0.8 -0.4 0 0.4 0.8 1.2 1.6 2 Voltage Output / V 13.55 13.56 13.01 8.7 4.43 0 -4.21 -8.09 -12.14 -12.78 -12.82 Satur ation of an Op-am p in the Inve r ting M ode 15 Op-amp is saturated The gain equation works well on this part of the graph. 10 Voltage Output / volts 5 0 -2.5 -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 -5 -10 -15 V oltage Input / volts Op-amp is saturated 2.5 Saturation • The op-amp will saturate if the input voltage is increased too much or if the gain is increased too much.